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At key-on, the Powertrain Control Module (PCM)
sends out a regulated 5 volt signal to the ECT sensor.
The PCM then monitors the signal as it passes
through the ECT sensor to the sensor ground (sensor
return).
When the engine is cold, the PCM will operate in
Open Loop cycle. It will demand slightly richer airfuel
mixtures and higher idle speeds. This is done
until normal operating temperatures are reached.
The PCM uses inputs from the ECT sensor for the
following calculations:
² for engine coolant temperature gauge operation
through CCD or PCI (J1850) communications
² Injector pulse-width
² Spark-advance curves
² ASD relay shut-down times
² Idle Air Control (IAC) motor key-on steps
² Pulse-width prime-shot during cranking
² O2 sensor closed loop times
² Purge solenoid on/off times
² EGR solenoid on/off times (if equipped)
² Leak Detection Pump operation (if equipped

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When the engine is at operating temperature, this
is a Closed Loop mode. At cruising speed, the PCM
receives inputs from:
² Air conditioning select signal (if equipped)
² Air conditioning request signal (if equipped)
² Battery voltage
² Engine coolant temperature sensor
² Crankshaft position sensor
² Intake manifold air temperature sensor
² Manifold absolute pressure (MAP) sensor
² Throttle position sensor (TPS)
² Camshaft position sensor signal (in the distributor)
² Park/neutral switch (gear indicator signal—auto.
trans. only)
² Oxygen (O2S) sensors
Based on these inputs, the following occurs:
² Voltage is applied to the fuel injectors with the
ASD relay via the PCM. The PCM will then adjust
the injector pulse width by turning the ground circuit
to each individual injector on and off.
² The PCM monitors the O2S sensor input and
adjusts air-fuel ratio. It also adjusts engine idle
speed through the idle air control (IAC) motor.
² The PCM adjusts ignition timing by turning the
ground path to the coil on and off.
² The PCM operates the A/C compressor clutch
through the clutch relay. This happens if A/C has
been selected by the vehicle operator and requested
by the A/C thermostat.

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